7 Biology - Genetics, Populations, Evolution & Ecosystems

Community

All populations of different species living in the same habitat

Uniformly distributed

Same number of organisms in each region

Ecosystem

All the organisms living in a community plus all the non-living conditions in the area in which they live

Advantage of species having different niches

• Less competition for food / named resource

• Less interspecific competition

Niche

The role of a species within a community

Advantage of showing standard deviation

• SD is spread of data around the mean

• SD reduces the effect of anomalies;

• SD can be used to determine if the difference is significant;

Can you conclude that […] causes […]?

• A correlation does not indicate a causal relationship;

• As may be due to another [named] factor;

Describe succession.

• Colonisation by [named] pioneer species;

• Pioneer species changes the abiotic conditions;

• Environment becomes less hostile / more suitable for other species;

• Decrease in […] and increase in […];

• [Named] pioneer species outcompeted by […];

• ·Change in biodiversity;

• To [named] climax community;

Succession

Change in a community over time due to changing species & abiotic factors

Climax Community

a stable community with no further succession.

Feature of a climax community

• Stable community over long time;

• Abiotic factors relatively constant;

• Populations stable around carrying capacity;

Which community will be most stable?

• One with the most species present;

• More complex food webs;

Explain changes that happen during succession.

• Decrease in % cover of bare ground due to increase in plant coverage;

• Increase in species diversity as abiotic conditions less hostile;

• Increase in depth of soil as plants die;

• Increase in total number of organisms;

• Greater variety of food sources;

• More variety of habitats;

Describe random sampling.

• Used when conditions are the same in the sample area;

• Divide area into squares;

• Draw random co-ordinates out of a hat;

• Count number / % cover in a quadrat;

• Large sample and calculate mean;

• Multiply mean per quadrat by number of quadrats in area;

Describe systematic sampling.

• Used when abiotic conditions change over a distance;

• Quadrats placed at intervals along transect;

• From […] to […];

• Count number / % cover in a quadrat;

• Repeat with more than one quadrat at each interval;

• Calculate the mean and standard deviation;

How to know how many quadrats to use.

• Calculate running mean;

• When enough quadrats mean levels out;

• Enough to carry out statistical test;

• A large number so results are reliable;

Why use random sampling.

• Avoids bias;

• Allows use of statistical tests;

Suggest why % cover used

• Difficult to count individual organisms;

Intraspecific competition

competition between individuals of the same species.

Interspecific competition

competition between individuals of different species.

Things organisms compete for:

• Food / water;

• Resources;

• Mates / territory;

Describe mark-release-recapture.

• Capture sample, mark and release;

• Ensure marking is not harmful to organisms;

• Allow time for organisms to randomly distribute before collecting a second sample;

• Take 2nd sample & count marked organisms;

• Population = (number in first sample x number in second sample) ÷ number of marked recaptured;

Why large lake may give unreliable results.

• Less chance of recapturing organisms;

• Unlikely organisms distribute randomly;

Assumptions made in mark-release-recapture.

• Animals are all from the same population;

• No immigration / emigration;

• No reproduction;

• Sample is large enough;

• Sampling method is the same;

Abiotic factor

non-living factor.

Biotic factor

living factor.

Explain abiotic factors.

• Carbon dioxide linked to photosynthesis;

• Light linked to photosynthesis;

• pH linked to enzymes;

• Temperature linked to enzymes;

• Water for growth;

• Wind linked to damage;

Explain biotic factors.

• Competition – fighting over resources;

• Decomposers – break down dead organisms;

• Disease – illness causing abnormal function;

• Grazers – animals that feed on plants;

• Humans – causing deforestation;

• Predation –organism killing & eating another;

Reasons for conserving woodland.

• Conserving habitats;

• Maintaining biodiversity;

• Reducing global warming;

• Sources of medicines;

• Reduces erosion & eutrophication;

When evaluating research.

• Was a control experiment used?

• Were biotic / abiotic factors controlled?

• Was the experiment repeated?

• Was there a statistical test?

• Could there be other factors affecting this?

Effect of non-native species.

• No consumers / pests / predators / pathogens;

• Out-competes / kills / eats native species;

• Some populations of native species become extinct;

Economic consequences of invasive species.

• Cost of removal;

• Cost of restoring habitat;

• Loss of income from tourism;

• Loss of income from fishing;

Microbe growth curve.

• Increase in population;

• Increase in uptake of oxygen & glucose for growth;

• Aerobic respiration releases energy;

• Glucose / oxygen becomes limiting & cells die;

Gene Pool

all the alleles in a population.

Population

A group of organisms of the same species living in a particular area at a particular time.

Species

a group of similar organisms able to reproduce to give fertile offspring.

How to use the Hardy-Weinberg equation.

• Use […] to find frequency of homozygous recessive q2;

• Find square root of q2 to get q;

• Use of p + q = 1.0 to determine frequency of p;

• Use of 2pq to find heterozygous;

What the Hardy-Weinberg principle predicts.

• The frequency of alleles of a particular gene;

• Will stay constant from one generation to the next;

• If there is no mutation / no selection / a large population / geographically isolated / mating at random / no migration;

Allopatric speciation

Formation of a new species from different geographically isolated populations.

Sympatric speciation

Formation of new species from the same population without geographical isolation.

Describe allopatric speciation

• Geographical isolation;

• Separate gene pools;

• Mutation causes […] / genetic variation;

• Different selection pressures;

• Differential reproductive success;

• Change in frequency of alleles;

• Eventually different species cannot interbreed to produce fertile offspring;

Describe sympatric speciation

• 2 species evolving in the same habitat;

• Mechanism of reproductive isolation described;

• Mutation causes […] / genetic variation;

• Different selection pressures;

• Disruptive natural selection;

• Change in frequency of alleles;

• Eventually different species cannot interbreed to produce fertile offspring;

Explain high frequency of mutation in a population.

• Isolated so inbreeding;

• Allele inherited from common ancestor;

Explain why migration maintains genetic variation.

• Smaller gene pool;

• Migrants bring in new alleles;

Advantages of presenting data as a ratio.

• Allows valid comparison;

• As sample size may vary;

Genetic diversity

The number of different alleles of genes in a population. Differences in DNA in a gene pool.

Use of twin studies.

• Identical twins show genetic influence;

• Non-identical twins show environmental influence;

Selection pressures are caused by…

• Antibiotics;

• Competition;

• Disease;

• Predation;

Factors to control in twin studies.

• Age / gender / family history / use of drugs / ethnicity…

Stabilising Selection

• Selection against both extremes;

• For example human birth mass;

• Range decreases, mode stays the same;

Directional Selection

• Selection against one extreme;

• For example antibiotic resistance;

• Range stays the same, mode changes;

Disruptive Selection

• Selection favours both extremes;

• For example fur camouflage;

• Range increases, two modes found;